(04-22) 18:48 PDT SAN FRANCISCO -- LinkedIn has leased a 26-story South of Market skyscraper, the latest in a string of big real estate wins for San Francisco and another example of Silicon Valley's migration north into the city, officials said Tuesday.

LinkedIn declined to disclose financial terms of the deal, but said it plans to house as many as 2,500 employees in the tower now under construction at 222 Second St.

The Mountain View professional social networking company will rent about 450,000 square feet of office space in the fourth-largest known commercial real estate deal in the city's recent history, said Colin Yasukochi, director of research and analysis for commercial real estate brokerage CBRE.

Just this month, Salesforce.com agreed to the biggest deal, leasing 715,000 square feet in a new 61-story skyscraper under construction near the site of the old Transbay Terminal. The move to the new Salesforce Tower - slated to be the city's tallest - paved the way for Salesforce to sell its Mission Bay property to the Golden State Warriors for a new arena.

And Microsoft also confirmed this month that it plans to relocate its San Francisco office into 50,000 square feet of space at 555 California St. The tower is the second-tallest in the city and was formerly known as the Bank of America building.

Historically, tech companies have moved into low-rise buildings - like Twitter's 10-story Mid-Market Street structure - that offer a large amount of floor space to accommodate their typical collaborative, open-office decor, Yasukochi said.

But increasingly, tech companies are moving into buildings taller than 10 stories that used to house other industries, such as legal, financial and accounting firms, he said.

That's despite commercial real estate rates that average $57 per square foot per year, 86 percent higher than they were in early 2010.

Like LinkedIn, tech companies are competing for employees who want to work in the city near amenities like restaurants and public transit, which are closer to San Francisco's skyscrapers, he said.

A recent CBRE survey showed that tech firms occupy about 17 million square feet of office space in the city "and 45 percent of that was in high-rises, which was a surprise for us," Yasukochi said.

In LinkedIn's case, the company wanted to consolidate its San Francisco offices housing several hundred employees, said Hani Durzy, director of corporate communications.

"We're a fast-growing company, and having this space gives us the room to grow in San Francisco and have greater access to the talent that is in the northern part of the Silicon Valley," he said.

The company now leases 135,000 square feet in the One Montgomery Tower and plans to lease 87,000 square feet of space on Howard Street until the new tower is open.

LinkedIn operates a professional social network with 300 million members, two-thirds of them outside of the United States. It has more than 5,000 employees worldwide, and plans to keep its headquarters in Mountain View. About 2,000 employees work in that facility, but the company is also building offices in Sunnyvale.

New York commercial real estate development firm Tishman Speyer began construction at the corner of Second and Howard streets last year. The tower is scheduled for completion in 2015, with LinkedIn set to move in early 2016.

LinkedIn had looked at expanding into about 250,000 square feet of space in another Tishman Speyer building on Howard in a deal that involved CBS Interactive, Yasukochi said.

That deal didn't materialize, but it opened the door for the new tower.

A Tishman Speyer spokesman declined to comment on the project beyond a press release issued by San Francisco Mayor Ed Lee.